Linear actuators are used for raising and lowering e.g. a piece of furniture, e.g. the height of a table top. A linear actuator may comprise a drive shaft, a transmission connected to the drive shaft and a spindle connected to the transmission, wherein the drive shaft, the transmission and the spindle are connected in such a way that a rotational movement of the drive shaft is transmitted to the spindle via the transmission. The linear actuator further comprises a spindle nut arranged rotationally prevented onto the spindle such that the spindle nut moves along the spindle when the spindle is rotated.
In such arrangements there is a need to stop the raising movement when a predetermined uppermost position is reached, and to stop the lowering movement when a predetermined lowermost position is reached. This is to avoid that the linear actuator is driven into its physical end positions, which may result in damages to the linear actuator.
There are many kinds of prior art end stop detection systems. WO2009039853 shows a system for detecting that the spindle nut reaches its predetermined end positions. This system uses capacitive detectors connected to end stop switches arranged in the leg, in parallel with the spindle. The system is used to detect when the spindle nut reaches the predetermined end position and to prevent further movement in that direction when the predetermined end position is reached.
Such a system requires a lot of the limited space available in the legs. Further, the system is rather complicated and expensive.
Consequently, there is a need for an alternative, cost-efficient and secure way of detecting that a spindle nut of a linear actuator reaches a desired end position.